Production of vulcanized rubber and accelerators therefor



Patented Dec, 7', 1926.

UNITED STATES PATENT OFFICE.

HAROLD WALTER ELLEY, OF WILMINGTON, DELAWARE, ASSIGNOR TO E. I. DU PON'I' DE NEMOURS & COMPANY, OF 'WILMINGTON, DELAWARE, A CORPORATION OF DELAWARE.

PRODUCTION OF VULCANIZED RUBBER AND ACCELERATORS THEREFOR.

No Drawing.

This invention relates to the vulcanization of rubber, to a new class of or anic accelerators for use in the vulcanization process, and .to the rubber compounds obtained by such process. Y

I have discovered that methylene-bisaminodithionic acid (that is methylene-bisdithiocarbamic acid) and its various derivatives-such as its homologues, salts, and

10 anhydrides-constitute, as a class, vulcanization accelerators of an extremely active type. Defining the new accelerators by reference to their molecular structure, it may be said that the molecules of the-various l5 specific accelerators have in common the following atomic grouping:

each of the two end carbon atoms being attached to another sulfur atom, as shown in the following graphical partial formulas:

Application filed February 25, 1925. Serial No. 11,590.

where M stands for a divalent metal such as zinc or lead; or, more generically,

where M represents a metal and n stands lor the valence of said metal. v

The more valuable accelerators of this subclass have the following general graphical formula: w

where R and R stand. for hydrocarbon radicals, and R and R stand for hydrogen or hydrocarbon radicals. Y

Examples of accelerators of this subclass are the alkylidene-bis-alkylamino-dithionates such as:

Methylene-bis-methylamino-dithionate of zinc om--N-ose z HdH n Butylidene-bis-methylamino-dithionate of 80 and the alkylidene bis-aralkylamino-dithionates suchas:

Ethylidene-bis-benzylamino-dithionate OuHFCHx-N-CS .om- -bn Zn can-om- -css' 2. Methylene-thiunam-disulfide and its homologues and derivatives, all of which probably contain the "following atomic grouping ear Y These compounds are readily obtainable from the corresponding sodium dithionates by oxidation in accordance with the following equation:

Valuable accelerators of this subclass are the alkylidene-dialkyl (or diaryl)-th iu-ramdisuliides having the following general graphical formula:

where R and R stand for hydrocarbon radicals and R and R stand for hydrogen or hydrocarbon radicals.

Examples of accelerators of this "subclass are:

'Methylene-dimethyl-thiuram-disulfide, Ethylidene-dibenz l-thiuram-disulfide, Butylidene-diethy-thiuram disulfide. 3. Methylene-thiuram-mono-sulfide and its homologues and derivatives, the molecules of which probably contain iii-common the 'following atomic grouping:

Valuable accelerators of this subclass are believed to have-the following general formula:

ide, the reaction apparently proceeding in accordance with the following equation:

s -N-li-s Accelerators of this third group which are particularly valuable are the alkylidenedialkyl o-r diaryl thiuram=m011osulfitlcs hav ing most probably the following general graphical formula:

this purpose has been greatly restricted because many rubber stocks containing such accelerators cannot be conveniently handled without excessive scorching. The new accelerators which I have discovered and described above, however, although extremely active, are free from'the objection above mentioned. Whilemy accelerators are able to efiect vulcanization at temperatures above (3., they, nevertheless cause practically no scorching as a result of mill- 1 ing. Moreover, these new types of accelerators not only give eflicient cures at a temperature corresponding to five pounds steam .pressure, but also show excellent accelerating power at the usual vulcanization temperatures, that is, corresponding to forty pounds steam pressure. The great accelerating power ofmy accelerators throughout a re markably wide range of curing temperatures, and the exceedingly slight tendency to where R and R stand for hydrocarbon radicals, and R and R stand for hydrogen or hydrocarbon radicals.

These mono-sulfides may beobtalned from the corresponding disulfides described under subclass 2 above by treating the disulfide with an alcoholic solution of potasslum cyanscorch during milling renders these accelerators of great importance commercially.

The vulcanized rubber obtained by my process possesses remarkably high tensile strength, resistance to tear, elasticity, and good ageing qualities. My accelerators do not discolor the stock, do not give an ofi'ensive odor to the rubber, and do not give ofi' cible solvent such as dilute alcohol.

Ewam-ple 258 parts (by weight) of sodium methyldithiocarbamate are suspended or dissolved in 258 parts of water, and the resulting suspension or solution is mixed with 72 parts of normal butyraldehyde dissolved in amisresulting mixture is maintained at a temperature of from about to 80 C. for

about an hour, or until the reaction is' substantially completed. At-the end of this time, the sodium salt of butylidene-bismethyl-dithiocarbamate may'ioe isolated by concentrating the solution under diminished pressure. However, if it is desired to roduce a metal salt of the butylideneismethyl-dithiocarbamate, -for use directly, as an accelerator, the solution, instead of being concentrated may be treated "with the theoretical amount of zinc sulfate, after suitable dilution with water, to convert the sodium salt into the insoluble zinc, salt of butylidene-bis-m'ethyl-dithiocarbamate.

In this example the'condensation of the butyraldehyde with the sodium methyldithiocarbamate probably proceeds in ;accordance with the following equation:

I OHgNCSSNii 2CHiNHCBSNa+C;H1OHO- C H1 H 1+H,o.

. ,om CSSNa Another 'method of preparing these alkylide'ne-bis-alkyl-dithiocarbamates may .be 11 lustrated by the following example:

Ewm ze'lzi j 240 parts of' ethylidene-bis-benzylamine are treated with about 152 arts of carbon disulfide and 80 parts of so 'um hydroxide, the reaction probably proceeding in"acc0rdance with the following equation:

metalsalts o the correspondingalkylidenebis-alkylor aryl-dithiocarbamic acids by treating a cold solution of the latter with a halogen, for example, chlorine.

The

amples mentionin am les but includes broadly a dit The allfiylidene dialkyl or diaryl-thiurammono-sul des may be produced from the corresponding disulfides by a process analo-.

gous to that heretofore known, that is, by treating the disulfides with potassium cyanide in alcoholic solution, as shown ,in Ber.

36, (1903) page 2275.

Although, in the above description, the examples emphasize the importance of the alkylidene-bis-alkyldithiocarbamates and the corresponding thiuram disulfides-and monosulfides', our invention includes equally the alkylidene-bis-aryldithiocarbamates such as: Butylidene-bis-o tolyl 7 dithiocarbamates; and the corresponding aryl-thiuram sulfides Sl'l'GlYaS: i

and f Butylidene di o-tolyl-thiuram .monosuls ide. i

Butylidene di 0 tolyl-thiuram disulfide,

In using the abovedescribed accelerators, combined zinc-preferably in the form of zinc oxide-is advantageously incorporated in the rubber mix along with sulfur and accelerator. Typical. cures may be illustrated by the following examples:

2 Parts." Smoked "sheet 50 Amber crepe 50- Zinc oxide 6 Sulfur l 6 Zinc butylidene 7 bis methyl dithiocaran I . bamateu 1" The material is placed" in a mold and heated with steam at 5 pounds pressure (about C.) for 30 minutes when vulcaniza- (about 125 C.) for 20,minutes t e vulcanized product possessed a tensile strength of 4 065 pounds and an elongatiaflfiow. though in the above description the invention has been illustrated by s ecific ext.

I kylideneiocarbamates of metals, particularly divalentmetals, such as zinc, lead, copper, mercury, manganese, etc. and includes also sub-' stances having the generic formulas given above and containin in place of the specificalkylidene, aryl, an alkyl radi'cals, hereinbefore mentioned, various other analogousradicals.

Lclaim: 1 '1. A process of vulc'anizing rubber which comprises combining with the rubber a vulcertain speci c. acceler-. ators, it will be un erstood that my invention is not 1n any way lim ted to these specific ex- 4. A process of vulcanizing rubber which comprises combining with the rubber vulcanizing. agent and an alkylidenebis-dialkyldithiocarbamate of a divalent metal andsubject-ing the mixture to a vulcanizing tempera ture.

5. A vulcanized rubber obtainable by sub jecting to a vulcanizing temperature a mixture of rubber, a vulcanizing agent, and an accelerator whose molecules contain the "following atomic grouping:

each of the two end carbon atoms being at-- tached to another sulfur atom.

6. A process of vulcanizing rubber which comprises combining with the rubber an ac-- celerator whosemolecules contain the following atomic grouping:

each of the two end carbon atoms being attached to another sulfur atom, and a vulcanizing agent in the presence of. combined. zinc, and vulcanizing the rubber.

7. A process of vulcanizing rubber which comprises mixing with the rubber a vulcanizing agent, combined zinc and an accelerator having a molecular structure indicated by the following general formula:

- R -N-c s s --M R- R n -l r-cksw-m where Band B stand for h drocarbon radi cals, R and R stand for by rogen or hydrocarbon radicals, M represents a metal, and n the .valence of said metal; and subjecting the resulting mixture to a vulcanizing temperature.

8. A vulcanized rubber obtainable by the process defined in claim 6. v

9. A-vulcanized rubber obtainable by the process defined inclaim 7.

10. A vulcanized rubber, obtainable by the process defined in claim 1, a

11. A processcf vulcanizing rubber which comprises mixing with the rubber a vulcanizin agent, COIHblIled zinc and an accelerator w lose molecules contain the following general atomic grouping where R- and R represent hydrocarbon radicals containing from 1 to 7 carbon atoms, R represents a hydrogen or ahydrocarbon radical containing from 1 to 4 carbon atoms, and R represents a hydrogen or hydrocarbon radical containing'from 1, to 1 carbon atoms, each of the end carbon atoms which are shown in the above grouping as being bound to sulfur atoms bein attached to another sulfur atom; and bjecting the resulting mixture to a vulcanizing temperature.

In testimony 'whereotl atfix my signature.

HAROLD WALTER ELLE i. 

